Elk browsing increases aboveground growth of water-stressed willows by modifying plant architecture

Johnston, Danielle B.; Cooper, David J.; Hobbs, N. Thompson

doi:10.1007/s00442-007-0854-4

Cited by 30 publications

(41 citation statements)

References 40 publications

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“…However, increased availability of water offers a plausible mechanism for these responses for two reasons. Photosynthetic rates of willows on undammed plots with deep water tables were limited by water availability [49], and isotopic analysis of water use by willows adjacent to our plots showed clear positive correlations between height and access to groundwater [24]. Tercek et al [50] observed that tall willows had twice rspb.royalsocietypublishing.org Proc R Soc B 280: 20122977…”

Section: Discussionmentioning

confidence: 99%

Stream hydrology limits recovery of riparian ecosystems after wolf reintroduction

2013

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Efforts to restore ecosystems often focus on reintroducing apex predators to re-establish coevolved relationships among predators, herbivores and plants. The preponderance of evidence for indirect effects of predators on terrestrial plant communities comes from ecosystems where predators have been removed. Far less is known about the consequences of their restoration. The effects of removal and restoration are unlikely to be symmetrical because removing predators can create feedbacks that reinforce the effects of predator loss. Observational studies have suggested that the reintroduction of wolves to Yellowstone National Park initiated dramatic restoration of riparian ecosystems by releasing willows from excessive browsing by elk. Here, we present results from a decade-long experiment in Yellowstone showing that moderating browsing alone was not sufficient to restore riparian zones along small streams. Instead, restoration of willow communities depended on removing browsing and restoring hydrological conditions that prevailed before the removal of wolves. The 70-year absence of predators from the ecosystem changed the disturbance regime in a way that was not reversed by predator reintroduction. We conclude that predator restoration may not quickly repair effects of predator removal in ecosystems.

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Section: Discussionmentioning

confidence: 99%

Stream hydrology limits recovery of riparian ecosystems after wolf reintroduction

2013

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“…The August xylem pressure potentials corresponded to an approximate 25% loss of hydraulic conductance in S. geyeriana shoots (Johnston et al 2007). Therefore, the plants experienced considerable late season water stress.…”

Section: Discussionmentioning

confidence: 99%

“…The suppressed willow communities created by heavy elk browsing may have competitively excluded beaver (Baker et al 2005, Hebblewhite et al 2005. Beaver and willow form a symbiotic relationship as beaver use willows for dam building, and the dams raise local water tables and stimulate willow productivity (Lindroth and Bath 1999, Baker et al 2005, Westbrook et al 2006, Johnston et al 2007. Where beavers had historically altered local water tables on the northern range, beaver abandonment was accompanied by channel incision through up to 2 m of alluvial sediments (Wolf et al 2007).…”

Section: Introductionmentioning

confidence: 99%

“…Height recovery was chosen as a response variable because the height of willows in our study area (0.7 m in spring) was well below the typical stature of 3-5 m for the study species (Brunsfeld and Johnson 1985). In this context, height recovery indicated that plants are able to compensate for tissue loss due to browsing by growing large, hydraulically efficient shoots that best support photosynthesis and continued growth (Johnston et al 2007, Bilyeu et al 2008). …”

Section: Introductionmentioning

confidence: 99%

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Relationships between groundwater use, water table, and recovery of willow on Yellowstone's northern range

2011

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Abstract. Excessive levels of herbivory, incision of stream channels, and climate warming are believed to be responsible for the decline of woody deciduous plants in riparian zones in western North America, declines that are likely to be associated with diminished biological diversity. In the northern elk wintering range of Yellowstone National Park, USA, overbrowsing by elk (Cervus elaphus), lowered water tables resulting from stream incision, and loss of activity by beaver (Castor canadensis) have been implicated in the decline of willow (Salix sp.) communities. Reducing elk browsing appears sufficient for willow recovery in some areas, but where water table changes have been dramatic, recovery may be slow or absent. The importance of water table changes is disputed because experimental results demonstrate water table limitations, but water table depth has failed to explain variation in willow height at landscape scales. One explanation for this apparent discrepancy is that willows that have survived intensive browsing by elk have maintained access to groundwater despite declining water tables. Using stable isotopes of water, we examined the relationships between groundwater use, water table depth, and height of heavily browsed Salix geyeriana. Salix geyeriana groundwater use varied from 30% to 80%, and was higher later in the growing season, when soil water was less available and shoot water potentials were lower. Late season groundwater use explained 26% of the variation in total height of willows (P ¼ 0.002), with taller plants using more groundwater. Water table depth explained only 8% of the variability in total height (P ¼ 0.051), with shorter willows having deeper water table depths. Groundwater use and water table depth were uncorrelated. Height recovery following a winter of heavy browsing was related to groundwater use, but not groundwater depth. We suggest that access to deeper water sources alleviates late season water stress, allowing for more rapid height recovery and higher total plant height. Variability in groundwater access may account for variability in height recovery at landscape scales.

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“…For resource managers, impacts from ungulates on vegetation are becoming a common management problem [105][106][107][108][109], while options for controlling ungulate populations by slaughter, translocation and reproductive control receive little public and/or government support [110]. Translocation receives the greatest level of public support, but disease concerns have reduced the safety of translocating wildlife [111][112][113][114].…”

Section: Discussionmentioning

confidence: 99%

Estimating Economic Carrying Capacity for an Ungulate Guild in Western Canada

Kuzyk¹,

Cool²,

Bork³

et al. 2009

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Elk Island National Park in western Canada provides an ideal case study for an economic carrying capacity estimate because it supports high density of four species of ungulates (11/km 2 ), lacks large predators, and is enclosed by a 2.1-meter mesh fence. This high density of ungulates has created persistent management challenges by altering vegetation structure and community composition. Using linear programming, we explored optimal allocation of forage resources for bison (Bison bison bison), moose (Alces andersoni), wapiti (Cervus elaphus manitobensis) and deer (Odocoileus virginianus and O. hemionus) to maximize ungulate biomass and numbers, when constrained by use of the major forage classes and minimum viable populations (MVP) of those ungulate species that do not cross the boundary fence (bison and wapiti). Maximum numbers of animals were achieved by a stocking combination dominated by deer and bison, whereas maximum biomass was attained when bison and moose were abundant but deer were absent. Wapiti remained at MVP during all solutions. Optimal solutions consistent with current ungulate densities were associated with 7 to 11% forage removal. This is less than normally assumed for sustainable forage use, and may reflect the need to account for other biotic and abiotic losses to forage in carrying capacity models for which ungulate densities can be constrained by availability of a preferred forage class (e.g., grass) as well as forage quality. This research extends the conventional animal-unit concept to multispecies systems and provides templates based on forage biomass allocation for resource managers facing similar problems of joint stocking in different environments.

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Elk browsing increases aboveground growth of water-stressed willows by modifying plant architecture

Cited by 30 publications

References 40 publications

Stream hydrology limits recovery of riparian ecosystems after wolf reintroduction

Stream hydrology limits recovery of riparian ecosystems after wolf reintroduction

Relationships between groundwater use, water table, and recovery of willow on Yellowstone's northern range

Estimating Economic Carrying Capacity for an Ungulate Guild in Western Canada

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